The present invention relates to a pyridine-free Karl Fischer reagent for the determination of water. The reagent comprises a dissolving agent for the sample to be investigated and a titrating agent. This invention also relates to a process for the determination of water using this reagent. The dissolving agent contains sulfur dioxide and a pyridine substitute in a solvent, and the titrating agent contains iodine in a solvent.
A number of proposals for replacing pyridine in the Karl Fischer reagent by other substances is known from the literature. In Anal. Chim. Acta 94, 395 (1977), sodium acetate is used as a substitute for pyridine. However, this entails certain disadvantages. Acetates are formed, for example, with the alcohol used as the solvent, water being liberated and naturally interfering with the water determination method. The solutions are therefore unstable and their blank values increase constantly.
In addition to acetates, alcoholates, phenolates and salts of weak organic acids are also mentioned as a substitute for pyridine in British Pat. No. 728,947. When the substances mentioned in this patent were checked, it was found that they are unsuitable as a pyridine substitute, partly because of insufficient solubility and partly because of inadequate stability of the prepared solutions. Furthermore, it is known that when pyridine is replaced by amines, stable end points cannot be obtained in the titration (Anal. Chem. 28, 1,116 (1956).
It is thus found from the state of the art that the replacement of pyridine by the mentioned compounds is not practical, since these reagents either are not sufficiently soluble or are unstable, or yield false results.